fix calculation sum column (finally!)

EvoCalculator.Core.Calculation/Columns/SumColumn.cs

@@ -50,17 +50,20 @@ namespace EvoCalculator.Core.Calculation.Columns
 
         public override void ComputeValues(decimal requiredValue)
         {
+            var DIFFICULT_CASE = _percentPaymentColumn.Values.Take(_percentPaymentColumn.Values.Length - 1)
+                .Any(x => x < 3 && x > 0);
+
             var goalSeek = new GoalSeek(this);
             goalSeek.SeekResult(requiredValue,
                 new GoalSeekOptions(
-                    startingStabPoint: Convert.ToDecimal(
-                        (_postValues.BaseCost.Value - _preparedValues.FirstPaymentSum) /
-                        _preparedValues.Nmper - 2)
-                    // , tineExplorePercentage: 10
-                    // , maximumAttempts: 100000
-                    , initialTineSpacing: 10m
-                    , focusPercentage: 50
-                    // , trimFinalInputValue: true
+                    startingStabPoint:
+                    (_postValues.BaseCost.Value - _preparedValues.FirstPaymentSum) /
+                    (_preparedValues.Nmper - 3) * (DIFFICULT_CASE
+                        ? 0.1m
+                        : 1m)
+                    , maximumAttempts: 1000
+                    , initialTineSpacing: DIFFICULT_CASE ? 10000m : 1000m
+                    // , focusPercentage: 50
                 ));
         }
     }